The conventional lead grid plates for battery are generally manufactured by means of metal molds. The thickness of such cast grid plates is more than 1.2 mm. Moreover the thickness of the transverse and vertical members inside the grid plate frame is more than 0.8 mm. It is impossible to make them thinner, because any attempt to make them thinner results in a product partly lacking their grid constituent members.
In other words, in the casting process, it is impossible to ensure that the molten lead alloy reaches every part of the metal mold even when the temperature of the mold is high. This results in the production of unusable lead grid plates.
Yet, requirement for lead grid plates that are thinner than 1.2 mm recently arised to make it possible to have more electrodes in one container for the purpose of increasing the capacity of battery and also reducing their weight.
In addition to above-stated shortcoming, the casting process is not suitable for continuous mass production in terms of cost and efficiency. It is another shortcoming of the casting process that the dimensional precision of the cast product is inferior and this presents a problem in the automation of battery assembling processes.
In order to eliminate such shortcomings of the casting process, it is conceivable to manufacture lead grid plate through a press punching process. However, although the press punching process permits making the width of the grid forming member about 1 mm when the plate thickness is more than 1.2 mm, it is extremely difficult to make the width less than 1 mm when the plate thickness is less than 1 mm. However, with the width of the grid forming members wider than 1 mm, the amount of the active material that can be retained by the lead grid decreases. Then, with the retaining amount decreased, there is no sense in exerting the effort to make the lead grid plate thinner.
Generally, is punching a metal plate of iron, aluminum, etc. into a grid shape by means of a press, it is impossible to make the width of the grid forming members about the same as the thickness of the plate. Besides the lead alloy which is employed in manufacturing the lead grid plates for batteries is softer than iron, aluminum and other metals. This makes the press punching more difficult. The deformation and breakage of the structural members of the grid tend to take place in the punching process. It is thus difficult to obtain usable lead grid plates. This tendency is more stronger with a thin plate measuring less than 1 mm thickness and with narrow grid forming members measuring less than 1 mm width.
This invention solves these problems. In accordance with the invented method, the thickness of the lead grid plate can be decreased to about 0.6 mm and the width of the grid forming members also can be reduced to about the same as the thickness. This is impossible by the conventional casting method. Besides, the invented method makes possible continuous production processes including preparation of lead grid plates from strips of a lead alloy obtained by a continuous casting process, filling the grid windows with an active material paste and obtaining dried, filled plates.